1. Field of the Invention
The present invention relates to a three-axis acceleration switch array.
2. Description of Related Art
There is a need for acceleration sensor that can be used for traumatic brain injury (TBI) monitoring for extended periods of time and in a very small and lightweight package. Preferably the package would be small enough to be inserted into an earplug or affixed to the skin with adhesive tape. Such a switch could also have relevant applications in package surveillance, shipping damage sensing, inertial wake-up switch for persistent low-power sensing systems, security system wakeup/trigger for vehicles, airbag deployment sensors, impact or contact detection in robotics, munition target impact detection, and many more.
The relevant acceleration threshold ranges, specific to TBI, are approximately 30 g-300 g with a time resolution of 100 microseconds or faster.
There have been previously known acceleration sensors which have been fitted to helmets, including helmets for both civilian and army applications. The monitoring for TBI using a helmet mounted acceleration sensor, however, is less than ideal since such helmets designed to absorb energy and lower the acceleration of the head. Consequently, accurate monitoring of the head acceleration for TBI monitoring cannot be achieved with helmet mounted acceleration sensors.
There have been many previously known small accelerometers. However, these previously known accelerometers have been active and thus require electrical power on full-time basis. Even with a low current draw, such accelerometers are simply inadequate for long term military use in very small systems with minimal space for batteries or other power supplies. This low power is an advantage for reducing the size of systems outside the scope of TBI as well for reduction size in overhead subcomponents as well.
A still further disadvantage of these previously known accelerometers is that such accelerometers have not proven either efficient or accurate in the measurement of the direction of the impact. However, for TBI monitoring purposes, the direction of the impact can be critical.